Some processes used in the bulk production of steel in oxygen converters with a basic lining or for the treatment of iron, carry out the injection of oxygen and other gases and additions of solid fluxes in the form of powder through tuyeres located at the bottom of said converter.
This way of injection in the processes of steel production has acquired an increased importance due to its metallurgical and final product quality advantages. Within all the variants for the processing of liquid iron is the injection of powdered carbonaceous materials pneumatically conveyed into the liquid bath through the converter bottom tuyeres. The carbon thus injected goes into solution in the liquid metal, and reacts with the oxygen in the bath. The oxygen is injected through the converter bottom tuyeres or through a top lance. The reaction between carbon and oxygen produces CO and liberates heat and thus, a net energy input to the metal bath is carried out by said powdered carbonaceous material injection, favoring the process thermal balance.
In order to be able to introduce the powdered carbonaceous material or alternatively an oxidizing gas into the liquid metal, a device for selecting one of said fluids located before the converter bottom tuyeres must be used. This is because it is convenient that through the tuyere or tuyeres through which the carbonaceous material is injected, oxygen can also be injected when the carbonaceous material is not needed, i.e., that oxygen can be injected during the no-injection period of carbonaceous material and vice versa through the same tuyere that leads one of the fluids to the liquid metal bath.
The introduction of oxygen or alternatively carbonaceous material through the same conduit, for example, the mentioned tuyere for injection into liquid iron, implies the risk of explosions if the powdered carbonaceous material and oxygen come into contact under certain conditions likely to occur in some cases. This sets up the necessity of a highly safe mechanism able to lead carbonaceous material or alternatively oxygen into the same conduit.
It may be thought that the injection of the carbonaceous material and oxygen be carried out through independent conditions, i.e., certain tuyeres assigned to one fluid and other tuyeres to the other fluid. Unfortunately this arrangement has the inherent disadvantage that during the no injection periods of the carbonaceous material, the duct or tuyere would have to introduce an inert gas whose function would be to avoid the clogging of the tuyere tip by the penetration of the liquid metal, with the consequent thermal ballast and waste of an expensive gas. This is the reason behind the use of a mechanism which allows the use of the same conduit to transport oxygen and the carbonaceous material alternatively.
In the previous art concerning the alternative injection of powder, particularly carbonaceous powder material and an oxidizing gas, U.S. Pat. No. 4,552,334 discloses a device or valve for changing over of fluids and for selecting one to be injected in the converter. Such device has some inconveniences related to design and operation. For instance, one of the main problems related to the design of pneumatic transport systems is the wear of certain components along the transport line, and the worst is the frontal hitting of the solids against the metal in a 90.degree. elbow when a change of flow direction is required; in these cases the wear of a common elbow might be critical. The case of the device disclosed in said patent is very similar. In FIG. 1 a drawing of this valve device is presented in such position and mode of operation that a stream of solids/gas mixture flows through passageway (a) and in changing the direction, said solids hit the deflecting side (b) of such passageway (a) inside the ball valve, resulting in wear of such side and becoming critical when some abrasive material is injected, as for instance carbonaceous material.
Another inconvenience in said patent design is the possible entrapment of powder in the purge conduit (c). For instance, when powder is transported for injection through passage-way (a), it might be entrapped inside conduit (c) and when the change-over takes place to inject the alternative fluid through conduit (d) by rotation of ball (e), the entrapped solids in conduit (c) in some particular cases might not flow out, because when ball (e) rotates, the pressure difference along conduit (c) may not be enough, i.e., in rotation, entry port (f) and exit (g) of conduit (c) both receive certain pressure from the same source of purging gas, entry port (h); although entry port (f) has a bigger pressure, a critical case is when the entrapped solids are sticked or well agglomerated and the rapid rotation during the change-over gives no time for conduit (c) to be flushed. This situation results in a non desirable contact between solid fines, for instance carbonaceous material, and the alternative oxidizing gas.
Prior to the above mentioned art, U.S. Pat. No. 4,407,490 discloses a mechanism for similar application. In this case both inconveniences pointed out for the above described device are also evident: the stream of solid/gas mixture also hits a diverting wall, i.e., a solid disc seal in going through the valve when operated in the solid injection mode; also a possibility exists of mixing the carbonaceous material flow with the alternated flow during the switching operation from one fluid to another due to the fact that a common space does exist where the two fluids might be mixed.
In the two mentioned patents there is not shown a mechanism or direct way of indication of the precise position of the valve movable component so as to enable the control system to allow the flow of the desired fluid only when its single corresponding passage-way is correctly and precisely positioned for the flow of such fluid into the injection tuyere.
In the present invention a valve mechanism is presented for selecting one fluid from two arriving fluids separated by such mechanism for the continuous injection of gas or solid/gas mixture into a melt contained in a metallurgical converter, without the possibility of mixing the two fluids inside such valve by providing separated and independent paths for each fluid and comprising a completely straight path along the solid/gas mixture passage-way inside the valve and thus avoiding any wear effect by the stream of solids in passing through the valve components for injection.